Armadillo is a C++ linear algebra library (matrix maths) aiming towards a good balance between speed and ease of use. The API is deliberately similar to Matlab's. Integer, floating point, and complex numbers are supported, as well as a subset of trigonometric and statistics functions. Various matrix decompositions are provided through optional integration with LAPACK and ATLAS numerics libraries. A delayed evaluation approach, based on template meta-programming, is used (during compile time) to combine several operations into one and reduce or eliminate the need for temporaries.
The Parsing Expression Grammar Template Library (PEGTL) is a C++0x library for creating parsers according to a Parsing Expression Grammar (PEG). Grammars are embedded as regular C++ code, created with template programming (not template meta programming). These hierarchies naturally correspond to the inductive definition of PEGs. The library extends on the subject of PEGs with new expression types, actions that can be attached to grammar rules, and mechanisms to ensure helpful diagnostics in case of parsing errors. PEGs are superficially similar to Context-Free Grammars (CFGs).
libposix is an impementation of the core functionality of all Unix systems. It is a full, cross-platform implementation of the POSIX 2008 standard. It is meant to replace existing implementations of a Unix system's core libraries. It is an exact implementation of POSIX 2008 and nothing else (no extensions, no previous POSIX versions). However, it works well with possible extensions to the core system functionallity (for example, GNU or BSD).
librouteros is a library that can be used to communicate with devices running RouterOS, a Linux-based operating system by MikroTik. A generic and low-level interface is provided to issue arbitrary commands to the device and receive replies. For some commands, high-level abstractions are provided to simplify communication. The library is thread-safe and reentrant-safe.